Ford’s revi­sion of the C-Max hybrid’s mileage rat­ing is spurring changes in how the EPA tests vehicles.

Ford Motor Co.’s announce­ment yes­ter­day that it would revise the fuel econ­omy rat­ing of its C-Max Hybrid to more closely reflect the actual mileage the vehi­cles gets may have been the final push needed to change the way vehi­cles are tested.

The Dear­born, Mich.-based automaker changed its offi­cial rat­ing from 47 mpg to 43 mpg and offered 32,000 C-Max dri­vers as much as $550 for their trou­ble. While the change is going to cost Ford for at least $12 mil­lion, it was the final push the Envi­ron­men­tal Pro­tec­tion Agency (EPA) needed to alter the system.

“We’re going to update general-labeling reg­u­la­tions,” Chris Grundler, direc­tor of the EPA’s Office of Trans­porta­tion and Air Qual­ity told USA Today. The update will cover “which vehi­cles need to be tested.”

Grundler also noted that the agency plans to increase the num­ber of vehi­cles it tests and is adding 30 employ­ees to do exactly that. He said it rep­re­sents a 40% increase in the num­ber of test­ing employees.

The EPA has repeat­edly tried to adjust its test­ing pro­ce­dures to cope with the mileage prob­lem, most recently in 2008. It should be noted that Ford fol­lowed the rules when it came to test­ing the C-Max as well as when it used the 47 mpg figure.

The EPA’s rules allow automak­ers to group sim­i­lar vehi­cles into cat­e­gories based on sim­i­lar engines, trans­mis­sions and weight class. Then use the high­est vol­ume vehi­cle in the class, which in the case of Ford was the Fusion hybrid. The Fusion hybrid, accord­ing to Raj Nair, Ford group vice pres­i­dent of global prod­uct devel­op­ment, gets 47 mpg.